Port lre fixes 1

[saghul]

Disclaimer: I used AI to port the patches, and then reviewed them myself.

• Fix RegExp.prototype[Symbol.split] to not coerce captures to strings
• Fix Regexp.prototype[Symbol.match] to use CreateDataPropertyOrThrow
• Adjust lastIndex to leading surrogate in unicode RegExp
• Make \x{N} a syntax error in escape sequences

[bnoordhuis]

Unsafe/unsound when the pointer is unaligned. Something like this is sound (assuming it's not readying before the start of the buffer, of course):

Suggested change

	const uint16_t *p = (const uint16_t *)cptr;
	if (is_lo_surrogate(*p) && is_hi_surrogate(p[-1])) {
	cptr = (const uint8_t *)(p - 1);
	}
	uint16_t c[2];
	memcpy(c, &cptr[-2], sizeof(c));
	if (is_lo_surrogate(c[1]) && is_hi_surrogate(c[0])) {
	cptr -= 2;
	}

The high/low surrogate checks look inverted though.